Operating Expenses (Schedule of Direct Operating Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Expenses [Abstract]
Ancillary and logistical service expenses	$ 11,682	$ 13,878	$ 46,242	$ 40,106
Employee compensation expenses	10,170	10,032	30,120	24,321
Buildings, facilities and technology expenses	1,990	1,872	7,280	5,819
Travel, advertising and promotion expenses	5,921	5,562	20,535	17,644
Other costs of services	3,290	2,117	8,566	6,203
Cost of Services, Total	$ 33,053	$ 33,461	$ 112,743	$ 94,093